The present invention relates generally to a lifting tool, and more particularly concerns a fluid powered tool adapted for underwater use in the spent fuel pits of nuclear reactor facilities to raise individual fuel rods within spent or damaged fuel assemblies for inspection.
Nuclear reactors of the type utilized in power generation incorporate a large number of fuel assemblies arranged in a suitable configuration. Each fuel assembly includes numerous fuel rods, each of which comprises a stack of fuel pellets inside a tube sealed by end plugs. The fuel rods are held in an organized array by a "skeleton" comprising grids spaced at lengthwise intervals, control rod guide thimbles interconnecting the grids and extending beyond the ends of the fuel rods, and top and bottom nozzles. The fuel rods are usually held in axial position by springs at the grids.
During initial installation and periodic shutdown of the reactor for refueling, the fuel rods are inspected for damage which might allow leakage and thus contamination of the primary coolant. It will be appreciated that the metal tubes of the fuel rods constitute the primary containment boundary for the radioactive nuclear fuel therein. Fuel rods may develop cracks, pin holes or other defects during service which must be detected; however, this is a difficult task. For one thing, the fuel rods are positioned in mutually closely spaced apart relationship and are integral parts of the fuel assemblies. Such inspection typically takes place in the spent fuel pit of the reactor facility where the irradiated fuel assemblies are submerged in neutron absorbing liquid such as water. It will thus be appreciated that inspection of irradiated nuclear fuel assemblies takes place under submerged and difficult conditions.
Fuel assemblies can also be subject to corrosion or wear, particularly at the points of contact between the fuel rods and the springs at the longitudinal grids. In order to inspect the fuel assemblies at these points, it is necessary to raise the fuel rods slightly to clear the area engaged by the springs for inspection by remote controlled camera. Heretofore, however, there has not been available a precision tool which is adapted for operation under water for selectively raising fuel rods in the fuel assembly for inspection. There is thus a need for such a device in order to facilitate this aspect of inspecting irradiated fuel assemblies while completely submereged.